Why Does My Furnace Keep Shutting Off? - McMillin Air - HVAC Experts

Why Does My Furnace Keep Shutting Off?

Does your furnace keeps shutting off after running for only a few minutes? Does it turn back on all of its own? If that sounds familiar to you, then the issue with your furnace could come from one of these three things: the heat exchanger, the flame sensor rod, or the size of your furnace. There are some quick fixes you can try on your own. You can change your furnace’s filter if it’s dirty. Then, you can also try opening all your air supply vents. Both these things can make your furnace work harder than it needs to, which can cause it to overheat and turn off. If it doesn’t work, you’ll need to call in a professional to help fix your furnace. Here is a more in depth look at the three things that could be causing your furnace problems!

The heat exchanger is overheating!

A common reason a furnace short cycles is because the heat exchanger, which is the part that heats your air, is getting too hot due to a lack of airflow. Once the heat exchanger overheats, it trips the high limit switch, which shuts the furnace down to protect it. If the high limit switch goes bad, the furnace won’t shut down and the heat exchanger will crack. The lack of airflow could be the result of a dirty air filter, closing air supply vents around your house, or a dirty blower wheel. If the filter gets too dirty, the blower will struggle to pull in enough air over the heat exchanger. Closing too many air vents can slow down certain blower types and therefore reduce airflow. Also, over time, the blower wheel collects dirt, slowing it down and therefore limiting how much air it can deliver over the heat exchanger. This is why we suggest the initial DIY fixes, which could solve the issue. To clean the blower, however, it’s best to call a specialist!

The flame sensor rod is dirty!

If your furnace tries to turn on multiple times before stopping for a while, the problem is probably a soot-covered flame sensor rod. You might be wondering what the flame sensor rod is and why does it being covered in soot can cause short cycling. Well, the flame sensor rod is a safety device designed to detect a flame in your furnace burners. If it does not detect a flame, it shuts the gas valve. Normally, this is a good thing for you, because if it didn’t shut the gas valve, your furnace could fill your home with gas. And one well-lit match could cause an explosion. However, if the flame rod gets covered in soot, it can’t accurately tell if there’s a flame or not, so it shuts the gas valve, even if there is a flame. No gas means no flame, which means no heat for you. The solution is pretty straightforward; clean the flame sensor rod. Since this isn’t an easy DIY job, you should definitely call a professional.

The furnace is oversized!

Has this short cycling problem been going on for years? Or did you just get a new furnace? If the answer to either of those questions is yes, then the problem may be that the furnace isn’t sized properly for your home. Furnaces need to be sized just right or you’ll have issues. For example, an oversized furnace will heat the home too quickly, causing it to turn off and on too often. If this is your problem, you have a few options depending on how old your furnace is. If it’s brand new, contact your installer about this issue so they can fix it. Some contractors will give you a labour warranty on their work, so give them a call to find out what your options are. If it’s old, usually meaning older than 15 years, consider getting a new furnace. Make sure that your contractor calculates the right furnace size for your home!

Short-cycling, or having a furnace turn off and on quickly and more often than you have programmed, is a big problem for homeowners. It’s not just incredibly annoying; heating bills can become ridiculously expensive if the inefficient heating pattern continues. So contact a professional so they can check what is causing your issue!


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